Venus
Venus, in astronomy, 2d planet from the sun; it is often called the evening star or morning star and is brighter than any object in the sky except the sun and the moon. Because its orbit lies between the sun and the orbit of the earth, Venus passes through phases like those of the moon, varying from a large bright crescent when the planet is near inferior conjunction (nearest the Earth) to a smaller silvery disk when it is at superior conjunction (farthest from the earth). Since its greatest elongation (the angle made between the sun, the earth, and Venus) is 47°, it can never be seen much longer than 3 hr after sunset or 3 hr before sunrise. Rotation Venus revolves around the sun at a mean distance of c.67 million mi (107 million km) in a nearly circular orbit, and its period of revolution is about 225 days. It comes closer to the earth than any other planet, being c.26 million mi (42 million km) away at inferior conjunction. Venus is often referred to as the sister planet of the Earth, because it is only slightly smaller in both size and mass. Several important differences, however, exist between the two planets. Surface Although Venus is covered with a thick blanket of clouds that hides its surface from view, much has been learned of the conditions on Venus from U.S. and Soviet space probes. These probes indicate a surface temperature of about 890°F (475°C) and an atmospheric pressure as great as 100 times that at the earth's surface. The thick atmosphere is composed mainly of carbon dioxide, with a slight amount of water vapor and a trace of nitrogen and other elements. The high surface temperature is assumed to result partly from the greenhouse effect; radiation passing through the atmosphere heats the surface, but the heat is blocked by the enveloping carbon dioxide from escaping back out through the atmosphere. The European Space Agency's Venus Express space probe began orbiting the planet in 2006; its instruments are designed primarily to study the Venusian atmosphere. Colonization Due to the extremely hostile conditions on the surface, current technology disallows any possibility of colonizing the surface of Venus in the near future. However there have been recent speculations about the possibility of developing extensive "floating cities" in the atmosphere of Venus in the future. This concept is based on the atmospheric conditions approximately fifty kilometres above the surface of the planet, where atmospheric pressures and temperatures are thought to be similar to those of Earth. Proposals suggest that manned exploration can be conducted from aerostat vehicles, followed in the longer term by permanent settlements. The existence of dangerous quantities of volatile acids at these heights, however, precludes any short term settlements. Landis has also suggested that should Venus be shielded from the sun, then over time its atmospheric heat would be radiated into space resulting in the majority of the thick atmosphere eventually raining out onto the surface leaving a planet better suited for terraforming and eventual settlement. Space Missions 1962 –Mariner 2 (US) –first successful flyby of Venus; confirmed high surface temperatures and pressures, a carbon dioxide rich atmosphere, continuous cloud cover, and the slow retrograde rotation of the planet. 1967 –Venera 4 (USSR) –first spacecraft to survive entry into another planet’s atmosphere. Returned atmospheric data, and deployed a parachute system to an altitude of 25km, becoming the first successful probe to perform in situ analysis of another planet’s environment. 1967 –Mariner 5 (US)–successful flyby returning data on magnetic fields and plasmas, as well as UV emissions from the atmosphere. 1969 –Venera 5 and 6 (USSR) –atmospheric probes detected the presence of nitrogen and oxygen. 1970: Venera 7 (USSR) –first soft-landing on Venus and the first time data was returned from a manmade object after landing on another planet. It measured a surface temperature of 475°C and a surface pressure of 90 bar. 1972: Venera 8 (USSR) –landed on Venus and was the first to measure wind speeds as it descended through the atmosphere (from 100 metres/second above 48 kilometres to 1 metre/second below 10 kilometres). 1974: Mariner 10 (US) –Venus flyby en route to Mercury; tracked global atmospheric circulation with visible and ultraviolet imagery. It was the first spacecraft to have an imaging system. 1975: Venera 9 and 10 (USSR) –First spacecraft in orbit around Venus. They photographed the clouds and looked at the upper atmosphere, while the landers returned the first black and white panoramic images of the surface. 1978-1992: Pioneer Venus 1 and 2 –included a large entry probe and three smaller entry probes, providing vertical profiles of the atmosphere. Also the first orbiter to make radar mapping of the surface. Over a decade, it recorded a 90% decrease of sulphur dioxide, possibly indicating a large volcanic eruption just before the arrival. 1978 Venera 11 and 12 (USSR) –successful landing on the surface, and detection of lightning and thunder. 1982: Venera 13 and 14 (USSR) –the landers sent back the first colour pictures of the surface. 1983: Venera 15 and 16 (USSR) –the orbiters provided radar maps and atmospheric analyses. 1985: Vega 1 and 2 (USSR) –released landers and balloons at Venus en route to Halley's comet that recorded winds running at 240 kilometres/hour. Landers provided precise temperature profiles down to the surface and in situ measurements of cloud composition. 1990-94: Magellan (US) –mapped 98 per cent of the surface of Venus using synthetic aperture radar, at a resolution of 300 metres per pixel. 1990: Galileo (US) –flyby en route to Jupiter. First spacecraft observations of Venus' lower clouds and spectral imaging of the night side near infrared emissions. 1998, 1999: Cassini-Huygens (US, ESA) –flybys en route to Saturn. 2006 –present: Venus Express (ESA)–the first European spacecraft to orbit Venus. 2006 and 2007: Messenger (US) –flybys en route to Mercury. 2010: Akatsuki (JAXA) –Japanese orbiter, failed orbit insertion but a second attempt will be made in 2015. 2015+: Bepi-Colombo (ESA) –with a scheduled launch in 2015, two flybys of Venus are planned en route to Mercury. Venusians The Venusians are probably a race of living magma that's all made of shifting lava. They most likely breathe carbon dioxide and have a body temperature of 800°F and weighing about the volume of water. See Also *Hecate (planet) Category:Planets